In the automotive field, heads up display (HUD) is a significant feature.

It's an integrated electronic display device that projects vehicle information such as speed, fuel consumption, engine speed, navigation, etc. onto the front windshield or other display medium for the driver to view. This helps reduce safety risks caused by the driver looking down or shifting their gaze.

HUD originated in the aviation field and was first applied in the automotive sector by General Motors in 1988. BMW was the first European automaker to equip with HUD in 2003, and since then, many automakers like Mercedes-Benz, Audi, Toyota, and Honda have also introduced models with HUD. The HUD market accelerated again with the launch of the industry's first mass-produced AR-HUD (Augmented Reality HUD) by the new Mercedes-Benz S-Class in 2020.

There are three generations of HUD. The first is C-HUD (Combiner HUD), which has a small imaging area and limited display information. It's installed as an accessory and may cause secondary injury to the driver in case of an accident. The second is W-HUD (Windshield HUD), the most widely used one, which projects driving information onto the front windshield through optical reflection, offering a larger display range and longer projection distance. The third is AR-HUD, a new technology that combines digital images with the real scene, providing more information and better practicality and technological sense.

The HUD system consists of two key components: the projection unit and the display medium. The projection unit integrates a projector, reflector, projection mirror, adjustment motor, and control unit. The control unit acquires vehicle condition and navigation information through the vehicle data bus and outputs the image through the projector. The display medium is responsible for imaging, mainly semi-transparent resin glass and the front windshield.

The principle of HUD is similar to slide projection. The image generated by the projector is reflected onto the front windshield through reflectors and projection mirrors, allowing the driver to obtain the projected information at a平視 angle. The light source is generated by the Picture Generation Unit (PGU), and the high-brightness image information is amplified and coupled through multiple planar or curved mirrors and finally reflected to the driver's eye area, known as the Eyebox. Long virtual image distance (VID) and large field of view (FOV) are core requirements of AR-HUD. AR-HUD superimposes the projected virtual image of driving information onto real objects to achieve deep integration. To achieve this, AR-HUD requires a virtual image to be projected at least 7m in front of the driver.

Currently, the projection technologies used in HUD mainly include TFT-LCD (Thin Film Transistor Liquid Crystal Display), DLP projection (Digital Light Processing), laser scanning projection, and LCOS (Liquid Crystal on Silicon) projection. TFT-LCD is widely used in W-HUD, while DLP is the most mature technology in the AR-HUD field, but it has a high cost. The AR-HUD solution based on LCOS is advancing rapidly and may become a dark horse in the future.

（圖/文/攝：太平洋汽車 整理于互聯(lián)網(wǎng)）